Initial Stage Of Aging Research Articles

Effect of Composition and Distribution of Phases after Aging on Stamp Ability for Aluminum Alloy D16 (AA2014) Sheets

The relevance of this research is connected to the increasing requirements for accuracy in stamped parts produced from aged aluminum alloys, and can also be applied for making layered composites. Indexed requirements can be provided by controlling the structure of sheet blanks, particularly by the phase composition and distribution behavior. Results of experimental research into the effect of aging modes on composition, dispersion behavior, and stamping number of sheet samples of the D16 aluminum alloy (AA2014) are presented. Heat treatment includes quenching from a temperature of 500°С into water of room temperature and further aging: natural aging for 7 days and artificial aging at temperatures of 50, 100, 150, and 200°С with a duration at each temperature of 15, 30, 60, 120, and 240 min. A method of estimating the quantity of the characteristics of dispersion phases is proposed for the microstructural picture. Stamp ability is evaluated using the stamping number, which is the ration between yield stress and tensile strength. It is found that increasing aging temperature and durance leads to the growth of the stamping number, which shows a low ability for sheet-stamping operations of alloy. Aging at 50°С did not lead to the sedimentation of dispersion phases for either optical metallography or scan electron microscopy. The inhomogeneity of phase dispersion inside the grain grows at the initial stages of aging, when durance is less than 1 h and temperature is 100, 150 and 200°С. Further increasing durance to 4 h leads to inhomogeneity decreasing. There is no correlation between the uniformity of phase dispersion and the stamping number. The chemical composition of phases plays the main role in stamping number, outside of phase-dispersion uniformity. The phase-composition changes depend on the mode of heat treatment: at an annealed and naturally aged state, the θ and S phase is sediment. After aging at a temperature lower 150°С after a short durance of less than 1 h, the θ, S and T phases are revealed; the θ phase appears after aging at temperatures higher than 150°C and long durance reaching 4 h.

The Microstructure Stability of Super304H Steel Aging at 750°C

The microstructure stability and the effect of microstructure evolution on the properties of Super304H steel aged at 750°C for different time were investigated. The results showed that the microstructure of the Super304H steel after aging at 750°C consists of primary matrix and large amount of precipitated phases. The main precipitates were Cu-rich phase, MX phase and M23C6 carbides in austenitic matrix during aging. The M23C6 carbides precipitate preferentially at grain boundaries, and then coarsening remarkably with increasing aging time. The MX phase was stable during the whole aging process. The Cu-rich particle is smaller than 10 nm at the initial aging stage, and then coarsen with increasing aging time. The strength and hardness increase obviously at the initial stage due to the interaction of Cu-rich phase, MX phase and M23C6 carbides precipitation strength, in which Cu-rich phase strengthen action is the dominant. Coarsening M23C6 carbides weaken the strength during aging.

Selenate redistribution during aging in different Chinese soils and the dominant influential factors

To date, few works have attempted to determine the effect of soil types on Selenium aging process and the possible influential factors. In this study, the differences in Se speciation distribution and availability in 15 Chinese typical agricultural soils were investigated using spiked selenate for the entire year. Results evidenced that after one year of incubation, Se transformed from soluble fraction to Fe/Mn oxides and organic matter bound fractions in neutral or alkaline soils (pH 7.09–8.51) and from exchangeable fraction to residual fraction in acidic soils (pH 4.89–6.82). The available Se content in all soils declined rapidly at the initial stage of aging, with most of the neutral or alkaline soils reaching equilibrium after 109 d, whereas the acidic soils reached equilibrium after only 33–56 d. The available Se content in soil decreased constantly during the entire aging process in S4 (Xinjiang Gray desert soil), S12 (Anhui Yellow brown earths), and S15 (Hunan Krasnozems). Elovich model was the best model (R2 > 0.80) in describing the Se aging process. Estimated time for exogenous Se reaching the distribution of available Se in corresponding native soils extended from 9.7 y to 50.2 y, indicating a much longer time was required for spiked soil to reach equilibrium. Soil pH was the most significant factor directly and negatively influencing the aging process (p < 0.05), while organic matter played a dual role on Se speciation. Results could provide reference for the selection of unified equilibrium time on Se-spiked experiment.

Effect of hot deformation on γ″ and δ phase precipitation of Inconel 718 alloy during deformation&isothermal treatment

A deformation&isothermal treatment is applied to investigate the effect of hot deformation on precipitation of γ″ and δ phase in Inconel 718 alloy. The results show the precipitation behaviors are tailored by the deformation temperatures that γ″ phase precipitation is accelerated at 800 °C in place of δ phase as for 900 °C. Deformation at 800 °C and 900 °C makes the precipitation peaks for γ″ phase shift towards lower temperatures to be 742 °C and 735 °C, while the precipitation peaks for δ phase moving towards higher temperatures to be 941 °C and 943 °C, respectively. When subjected to the deformation&isothermal treatment at 800 °C, the thus formed structure is composed of ellipsoidal, disc and irregular-shaped γ″ precipitates with sizes varying from 80 nm to 440 nm in the interior of broadened GBs, as well as dispersively ultrafine intragranular γ″ particles. As for the specimen deformed at 900 °C, the δ-phase precipitation is promoted under the effect of static recrystallization occurring at the initial aging stage, that granular, disc and needle-shaped δ precipitates with 7.5 vol % are generated in the limited duration of 1 h.

Precipitation behavior and phase transformation of hyper duplex stainless steel UNS S32707 at nose temperature

In this work, time temperature transformation (TTT) diagram, thermodynamic calculations and microstructure observations were performed to investigate the precipitation behavior of hyper duplex stainless steel UNS S32707 aged at nose temperature for various aging time up to 48h. The corresponding secondary phase transformation mechanisms were proposed. The results demonstrate that the precipitation kinetics of σ phase in UNS S32707 is very fast due to its higher Cr and Mo contents at nose temperature of 950°C. At the initial stage of aging, σ phase preferentially formed along the α/α and α/γ phase boundaries and then penetrated into α phase, resulting from the eutectoid reaction α→γ2+σ. Meanwhile, a few σ phases nucleated at the γ/γ phase boundaries. With the aging time prolonging, some σ phases nucleated within γ phase due to the decomposition of the supersaturated γ phase. In addition, a cellular structure consisting of lamellar σ and γ2 phase was detected during short term aging, and it gradually grew with aging time via cell boundary migration. After 30min and 6h aging, the lamellar σ phases in the cellular structure broke into small lamellas or into bending bars and evolved into blocky shapes. Most of rounded Cr2N particles formed at the σ/γ2 interfaces and were surrounded by σ and γ2 phase. A few rod-like Cr2N particles nucleate at γ/γ phase boundaries due to the low energy interfaces between Cr2N and γ phase. No Cr2N was detected in α phase, which was attributed to the fact that σ phase has much faster precipitation kinetics than that of Cr2N.

Detection of susceptibility to intergranular corrosion of aged super austenitic stainless steel S32654 by a modified electrochemical potentiokinetic reactivation method

The double loop electrochemical potentiokinetic reactivation method was modified and applied to detect the susceptibility to intergranular corrosion of super austenitic stainless steel S32654 aged at 1000 °C. The precipitation behavior was clarified, and the corresponding intergranular corrosion mechanism of aged S32654 was proposed. The microstructure demonstrated that σ phase, Cr2N and π phase nucleated at the initial stages of aging and gradually grew larger with increasing aging time. The degree of sensitization increased rapidly in the early stage of aging and then showed a slow increasing rate during long term aging stage, and no self-healing has been observed. Such modified double loop electrochemical potentiokinetic reactivation method could successfully characterize the relationship between microstructure evolution and intergranular corrosion susceptibility of S32654. The mechanism of intergranular corrosion was attributed to the Cr and Mo depletion adjacent to σ phase and π phase and the Cr depletion around Cr2N.

The Effect of Sc Addition on Microstructure in Mg-Gd Alloys

Traditionally, Mg-Gd alloys have been strengthened by dispersed precipitates. Several reports are available about Sc addition to Mg alloys for improving a creep resistance. In this research, aging behavior of Mg-Gd, Mg-Sc and Mg-Gd-Sc alloys including the same amount of solute elements were investigated to understand the effect of Sc on microstructures and mechanical properties during aging. Hardness measurement revealed that Sc addition delayed to form precipitate. Close inspection of TEM micrographs, β” phase formed at an initial stage of aging and β’ phase was observed at a peak-aged stage in Mg-Gd and Mg-Gd-Sc alloys. In Mg-Sc alloy, there is no evidence of precipitate formation during aging at 473K.

Precipitation Sequence of a SiC Particle Reinforced Al-Mg-Si Alloy Composite

In this study, the precipitation sequence of a 5 vol.% SiC particles reinforced Al-1.12 wt.%Mg-0.77 wt.%Si alloy composite fabricated by traditional powder metallurgy method was investigated by transmission electron microscopy and hardness measurements. The results indicated that the addition of SiC reinforcements not only suppresses the initial aging stage but also influences the subsequent precipitates. The precipitation sequence of the composite aged at 175 °C can be described as: Guinier-Preston (G.P.) zone → β″ → β′ → B′, which was confirmed by high-resolution transmission electron microscopy. This work might provide the guidance for the design and fabrication of hardenable automobile body sheet by Al-based composites with enhanced mechanical properties.

Microstructural evolution of Mn-based maraging steels and their influences on mechanical properties

The microstructural evolution in a set of Mn-based maraging steels (7–12wt% Mn) when aged at 460–500ºC for various durations up to 10,080min and the influences on mechanical properties are systematically investigated. The improved yield strength of peak-aged samples is attributed to the formation of Ni2TiAl precipitates and the precipitation strengthening is governed by Orowan mechanism. Segregation of Mn at grain boundaries in the initial aging stage resulted in severe intergranular brittleness. During further aging, accumulated Mn segregation leading to the formation of ductile lath-like reverted austenite removed the embrittlement and significantly improved the ductility. In the overaged condition, the steady work hardening after yielding compensates the loss of yield strength resulting from the coarsening of precipitates and softening of α′-martensite matrix. There was only limited evidence of the TRIP effect in the reverted austenite, indicating that work hardening was associated with other deformation mechanisms. Increasing the aging temperature or the Mn content of alloy that promotes austenite reversion was demonstrated to accelerate the improvement of ductility.

Thermal‐oxidative aging effects on the properties of long glass fiber reinforced polyamide 10T composites

The results of thermal‐oxidative aging effects on the properties of long glass fiber reinforced polyamide 10T (LGF/PA10T) composites were investigated. The composite samples were aged at 240°C in a heat‐blast oven. The aging times were 10, 20, 30, 40, and 50 days. The thermal‐oxidative aging resulted in decline of crystallization behavior, dynamic and static mechanical properties of the LGF/PA10T composites. These observations can be attributed to the decomposition of the molecular chain of PA10T resin, carbonization of the matrix and interfacial debonding between the glass fibers and matrix, as illustrated by scanning electron microscopy and FTIR spectra. At the initial stage of aging, the storage modulus and glass transition temperature first increased and then reduced, which indicated that there was slight crosslinking between the molecular chains. After aging for 50 days, the retention rates of tensile strength, flexural strength, and notch impact strength of the composite samples were 4.9, 6.3, and 9.4% lower, respectively, than that of the unaged samples; thus, it can be concluded that molecular degradation dominated and caused deterioration of interfacial adhesive strength between the fiber and the resin during the whole aging process. Therefore, the LGF/PA10T resin cannot serve for a long‐time at 240°C. POLYM. COMPOS., 39:2117–2125, 2018. © 2016 Society of Plastics Engineers

Continuous Hardening During Isothermal Aging at 723 K (450 °C) of a Precipitation Hardening Stainless Steel

The isothermal aging behavior of a cold-rolled precipitation hardening stainless steel has been studied at 723 K (450 °C) for holding times up to 72 hours. The precipitation hardening has been investigated using microhardness Vickers (Hv), thermoelectric power (TEP) measurements, and tensile testing. Microhardness compared to TEP measurements is more sensitive to detect the initial stages of aging. Two precipitation regimes have been observed: the first one related to the formation of Cu-clusters for aging times below 1 hour and a second one associated with formation of Ni-rich precipitates. The results show that the material exhibits an outstanding continuous age strengthening response over the aging time investigated, reaching a hardness of 710 ± 4 HV1 and an ultimate tensile strength (σ UTS) of 2.65 ± 0.02 GPa after 72 hours. Engineering stress-plastic strain curves reveal that the strength increases and the ductility decreases as the aging time increases. However, after prolonged holding times (24–72 hours) and, although small, a rise in both the strength and the total elongation is observed. The precipitation kinetics can be well predicted over the entire range of aging times by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. Finally, a reliable linear hardness-yield strength correlation has been found, which enables a rapid evaluation of the strength from bulk hardness measurements.

Stress relaxation ageing behaviour and constitutive modelling of a 2219 aluminium alloy under the effect of an electric pulse

In creep age forming (CAF), stress relaxation and the creep process occur during the ageing heat treatment. However, there is a remarkable difference between the deformation and phase transformation activation energies in aluminium alloys. To achieve high-performance and high-precision collaborative manufacturing of large-scale complex panels with high levels of reinforcement, the difference in the energy barriers between the stress relaxation process and the ageing precipitation process needs to be coordinated. An electric pulsed current (EPC) was first introduced into the CAF process for 2219 aluminium. It was found that the EPC can effectively regulate the stress relaxation behaviour during the initial ageing stage. That is, the application of EPC during the first 1 h of the ageing treatment process decreases the stress gradients for different initial stress levels, which makes it possible to reduce the deformation and phase transformation inhomogeneities resulting from stress differences inside a component under a bending load. Meanwhile, the apparent deformation activation energy decreases with the EPC, which decreases the energy barrier difference between the stress relaxation and ageing precipitation from 47 kJ/mol to 18 kJ/mol. Furthermore, the action mechanism for EPC on the stress relaxation process is discussed, and a constitutive model for stress relaxation age forming considering the effect of the EPC is established.

Effect of W Substitution on the Precipitation Behavior of χ and σ Phase in Super Duplex Stainless Steels

This study was carried out to investigate the effect of W substitution on the precipitation behavior of χ and σ phases in super duplex stainless steel. The χ phase was precipitated at the interface of ferrite / austenite phases and inside the ferrite phase at the initial stage of aging. With an increase in the aging time, the volume fraction of the χ phase increased, and then decreased with the transformation from the χ phase to the σ phase. The σ phase was precipitated later than the χ phase, and the volume fraction of x phase increased with the increase in the aging time. The ferrite phase was decomposed into the new austenite (γ2) and σ phases by aging treatment. The decomposition of the ferrite phase into the γ2 and σ phases was retarded by W substitution for Mo. The volume fraction of the χ phase increased and that of the σ phase decreased due to W substitution. The χ and σ phases were intermetallic compounds, which had lower nickel concentration, and higher chromium, molybdenum, and tungsten concentrations. The χ phase has higher molybdenum and tungsten concentrations than those of the σ phase. The amounts of chromium and nickel in the χ and σ phases did not change, but these phases have higher concentrations of molybdenum and tungsten due to W substitution for Mo.

Effect of aging time on intergranular corrosion behavior of a newly developed LDX 2404 lean duplex stainless steel

The effect of aging at 700 °C for various times on the intergranular corrosion behavior of LDX 2404 duplex stainless steel is investigated by morphological observation and electrochemical detection. Scanning electronic microscopy and transmission electronic microscopy analysis reveal that Cr2N, M23C6 and the sigma and chi phases nucleate simultaneously at the initial stages of aging. The granular particles of sigma phase grow larger but fewer with the increase of aging time. The electrochemical detection results show that intergranular corrosion become more severe and the corrosion type evolves from intergranular corrosion into general corrosion as the holding time extends to 48 h.

Effect of Aging Treatment on Impact Toughness and Corrosion Resistance of Super Duplex Stainless Steel

The effect of aging time on impact toughness and corrosion resistance of 25%Cr-7%Ni-2%Mo-4%W-0.2%N super duplex stainless steel from the viewpoint of intermetallic secondary phase variation was investigated with scanning electron microscopic observation with energy-dispersive x-ray spectroscopic analysis and transmission electron microscopy. The results clarified that R-phase is precipitated not only at the interface of ferrite and austenite but inside the ferrite at an initial stage of aging and then transformed into σ-phase from an aging time of 1 h, while the ferrite phase decomposed into γ2 and σ-phase with increase of aging time. This variation of the phases led to decrease of its impact toughness, and specifically, the R-phase was proved to be predominant in the degradation of the impact toughness at the initial stage of the aging. Additionally, these secondary phases led to deterioration of corrosion resistance because of Cr depletion.

Effect of aging time on corrosion behavior of as-forged AZ80 magnesium alloy

The corrosion behaviors of an as-forged AZ80 magnesium alloy after aging treatment for various durations at 170 °C were investigated by immersion test, H2 evolution test, SEM and potentiodynamic polarization curve measurement. The results show that the corrosion rate of the alloy decreases dramatically with the increase of aging time during the initial aging stage, but increases slowly with the aging time longer than 20 h. The volume fraction of β-Mg17Al12 increases with aging time within the first 20 h, leading to the decrease of corrosion rate. After aging for longer than 39 h, the growth of β phase is accompanied by the consumption of aluminum in the matrix, resulting in an increase in the corrosion rate. When the volume fraction of β phase is low, specimens suffer from severe local corrosion, which results in a porous surface. On the contrary, when the volume fraction of β phase is high, specimens suffer uniform corrosion attack.

B22-P-07Structural Analysis of Au Doped Titanium Disilicide using Cs-corrected Scanning Transmission Electron Microscopy

Al-Mg-Si-based alloys are widely used and studied due to the increasing demand of reducing weight of automobile body panels. One of the main topics in the studies is improvement of the hardening response in the initial stage of artificial aging. Recently, Koshino et al. reported that 0.04 wt.% addition of Li increases the hardness of an Al-Mg-Si alloy aged for not only 10 hours (peak aging) but also 20 minutes (under-aging) due to the co-segregation among Mg, Si and Li atoms [1]. The results had been predicted by early works [2, 3]. However, the effect of Li addition on microstructure evolution is not well understood. In this work, we conducted 3DAP analyses of a base alloy (Al-0.62Mg-0.93Si, wt.%) and a Li-added alloy (Al-0.55Mg-0.89Si-0.05Li, wt.%) aged at room temperature for 300 and 2100 hours. It was found that the Li-addition increases the number density of clusters which consist of mainly Mg and Si atoms. Further analyses were performed for the Li-added alloys to clarify the positional correlation between Li atoms and the clusters. Although it is difficult to judge the correlation visually as shown in Figure, co-segregation among Mg, Si and Li atoms was confirmed by applying statistical techniques.The detail of the analysis process will show in the presentation to discuss its superiority and limitation. [1] Y. Koshino, M. Kozuka, S. Hirosawa and Y. Aruga, J. Alloy Compd. 622 (2015) 765-770. [2] T. Sato, S. Hirosawa, K. Hirose and T. Maeguchi, Metall. Mater. Trans. A 34 (2003) 2745-2755. [3] S. Hirosawa, T. Omura, Y. Suzuki and T. Sato, Mater. Sci. Forum 215 (2006) 519-521. Figure: (a) Li, (b) Mg and (c) Si map of Al-Mg-Si-Li alloy aged at room temperature for 2100 hours. B22-P-07 doi:10.1093/jmicro/dfv263

Microstructure evolution and properties of Cu–20Ni–20Mn alloy during aging process

The microstructure evolution and phase transformation of Cu–20Ni–20Mn (mass fraction, %) alloy at 450 °C were investigated by X-ray diffraction and transmission electron microscopy (TEM). The variations of tensile strength, yield strength and hardness of this alloy during aging process were also analyzed. The results show that no significant variations of hardness and strength in the initial stage of aging, with a long incubation period, are observed at 450 °C. Subsequently, the ordered face-centered tetragonal (FCT) NiMn phase nucleates and grows up with prolonging the aging time. The hardness and tensile strength of the alloy increase up to their maximum values with increasing the ordered particle size, i.e., the strength of the alloy reaches 942 MPa after being aged at 450 °C for 40 h. The main cause of the age-hardening is considered to be precipitation strengthening due to the ordered FCT-NiMn particles.

Reliability study of industry Sn3.0Ag0.5Cu/Cu lead-free soldered joints in electronic packaging

The wettability of Sn3.0Ag0.5Cu on copper substrate with different reflow temperature was studied. The growth mechanism of intermetallic compound (IMC) and mechanical properties were also investigated under isothermal aging condition at 125, 150 and 175 °C with different aging time. The results showed that, with the reflow temperature increasing, the spreading area of Sn3.0Ag0.5Cu lead-free solder increased. The morphology of IMC formed at Sn3.0Ag0.5Cu/Cu interface was gradually changed from scallop-type to planar-type, and the thickness of IMC was increased with the aging temperature and aging time. Meanwhile, the IMC growth rate increased with aging temperature but decreased with aging time. In addition, the mechanical properties of solder joints with different isothermal aging decreased with increasing aging time. In the initial stage of isothermal aging, the mechanical properties of solder joints decreased rapidly, then the rate of decline became stabilized.

Influence of cold deformation and Ti element on the microstructure and properties of Cu–Cr system alloys

Abstract